The Missouri suburb of Ferguson looked like a war zone as torched buildings smouldered and angry crowds protested the police killing of an unarmed black teenager three months ago.

National Guardsmen rolled into town on military vehicles as part of a 2,200-strong security force.

In the quiet backstreet of Canfield Drive on Tuesday night, a group of teenagers in hooded sweatshirts loitered around the bouquets of flowers that mark the spot where Michael Brown was shot and killed by a white lawman in August - the latest race-relations tragedy to send shockwaves across the US.

"You want to know where the protesters are? We're the protests," one of a half-dozen teenagers told Al Jazeera, without disclosing his name. "You should get out of here. Maybe you ain't heard, but white people ain't so popular round here no more."

A few hundred metres up the street, police cars with blue flashing lights blocked the road in an effort to control the second night of protests since Monday, when a Grand Jury decided not to bring charges against the police officer responsible for Brown's death.

"There's a reason we're armed the way we are," said one officer, toting an assault rifle. "We figure we're gonna get shot at here at this roadblock. And if we go down there, there would be even more serious trouble. They got guns, too."

Unhappy history

Protests and mayhem in Ferguson, a suburb of St Louis of some 21,000 residents, were mirrored by demonstrations in Seattle, New York, Los Angeles and other US cities on Tuesday night, as the latest chapter of the US' unhappy history of race relations played out.

In New York, protesters briefly shut down the Brooklyn Bridge and disrupted traffic elsewhere. Hundreds blocked traffic in Cleveland, Ohio, in a separate demonstration over the fatal shooting of a 12-year-old boy by a police officer.

In Ferguson, rioters overturned a police car and set it ablaze while others hurled rocks at government offices on Tuesday night. As many as a dozen buildings were still smouldering alongside West Florissant Avenue, the site of many protests in recent months.

Officer Darren Wilson had been under investigation for the killing of Brown, an unarmed 18-year-old, whom he shot and killed during an altercation in a backstreet on August 9. He could have been charged with anything from involuntary manslaughter to first-degree murder.

Many in the African-American community had called for the officer to face murder charges but, after three months of closed-door talks, a randomly chosen Missouri grand jury of nine whites and three blacks decided against prosecution.

Self-defence?

Wilson had told investigators that he fired in self-defence after Brown pushed him back into his car, hit him and grabbed at his gun. During a television interview released on Tuesday, Wilson said he did not execute Brown and had a "clean conscience".

Benjamin Crump, a lawyer for Brown's family, told journalists on Tuesday the grand jury proceedings had been unfair because the prosecutor in the case had a conflict of interest, and Wilson was not properly cross-examined.

For many in Ferguson, this apparent lack of justice drove many protesters to the streets. According to Reverend Alvin Herring, from a group called People Improving Communities Through Organising, the anger witnessed in Ferguson shows how a mostly black community resents bullying at the hands of a police force that is 94 percent white.

"Michael Brown's body was riddled with bullets and left lying in the street for more than four hours," he told Al Jazeera. "The police response to a grieving and traumatised community was shameful: pointing military-grade weapons at unarmed young people, tear-gassing peaceful protesters and running police cars over Brown's memorial."

System 'out of control'

Anger over Brown's killing fits into a narrative of deep-seated race problems in the US that stretches back to the slavery era, through a civil rights struggle, and up to the election Barack Obama as the country's first black president six years ago.

Speaking in Chicago on Tuesday, Obama condemned the rioters, but also warned that concerns among ethnic minorities about a lopsided justice system are "rooted in realities that have existed in this country for a long time".

Comparable anger was evident after footage was aired of white Los Angeles cops beating Rodney King on the tarmac in 1991, and Trayvon Martin, a 17-year-old who was shot and killed in Florida in 2012 by a neighbourhood watch volunteer, who was acquitted.

"Shooting someone should have been the last resort, and not the first. These protests is gonna go on for a while. They can't keep on sweeping this under the rug," Carlos Mcduffie, 38, from Ferguson, told Al Jazeera.

"It's about a system that's been out of control since it was created, and there's nothing [that] can be done to change it."